Conventionally, at least one STI (shallow trench insulator) is provided between a P doped region and an N doped region to separate the P doped region and the N doped region. FIG. 1 is a semiconductor device 100 with a STI 101 for related art. As shown in FIG. 1, a STI 101 is provided between a P doped region 103 and an N doped region 105. Therefore, a current path CP for transmitting currents from the P doped region 103 to the N doped region 105 must by-pass the STI 101 since materials of the STI 101 are not conductive. In such case, the current path CP is longer, such that the charge/discharge time for the semiconductor device is correspondingly extended, which may causes some disadvantages. For example, if the semiconductor device 100 is applied as an ESD device, the circuit protected by such device is easily broken since the semiconductor device 100 has a low discharge speed.